CFD Verification of Engineering Options for Mitigating Liquid Sloshing in Topside Vessels on a Floating Production Facility

Abstract

This paper proposes an active-control concept that mitigates the liquid sloshing in a topside vessel by reducing the excitation source, thus extending the scope of sloshing mitigation. To verify the concept proposed, sloshing response in partially liquid-filled topside vessels was numerically investigated under various wave and vessel conditions. This study confirmed that vessel location on the top deck exhibits a weak correlation with the sloshing response. Although liquid sloshing is not very sensitive to the vessel location, it is beneficial to place the topside processing vessels as close as possible to gravity center of the floating production facilities (FPS/FPSO). It is evident that liquid sloshing in a topside vessel is closely related to the incident direction of the wave. The perpendicular incidence results in the minimum sloshing response; the parallel incidence leads to the maximum sloshing response. It is, therefore, essential to properly orient the vessel to establish perpendicular or close-to-perpendicular incidence status. It is also verified that liquid sloshing is significantly increased with length-to-diameter (L/D) ratio of a vessel. The horizontal vessels with larger L/D suffer from severe liquid sloshing. Because vertical vessels have a minimum L/D = 1.0, they always exhibit better antisloshing performance than the horizontal vessels. In addition, it is advisable to prevent a vessel from operating near the resonance-wave condition. Although the active control concept shows attractive advantages over the conventional approach, it is more feasible for layout of topside vessels on a newly built FPS/FPSO. Because most of the floating-production systems are not built from scratch such that the topside processing vessels can be placed in the optimal position and orientation but are retrofitted for a topside vessel to fit onto a limited deck space, the passive-control approach may be more applicable. Generally, combination of the active and passive approaches should be considered to minimize liquid sloshing in a topside process vessel.